1. Field of the Invention
The present invention generally relates to electronic monitoring systems. More specifically the present invention relates to an improved transmitting tag for enhancing the tracking and locating capability of a monitoring system and for allowing control over accessibility to particular zones and/or equipment within a restricted area. The present invention further relates to monitoring systems including the tag.
2. Discussion of the Related Art
Electronic monitoring systems for remote monitoring and supervising of moving objects, and in particular for monitoring persons, are known in the art. Such systems are employed for a wide range of applications in a variety of fields, including security, law enforcement, medical and more. A typical monitoring system comprises a plurality of portable transmitting devices, known as “tags”, one or more fixed or mobile local monitoring unit and a central monitoring station where the information received by the local monitoring units is collected and further processed. Each tag is having an identification code. The identification code may be a unique code specific to the subject with whom the tag is associated, such that the subject can be identified unequivocally. Alternatively, the identification code may be a code typical to a certain group. For example, in a hospital stuff may carry a tag of one identification code while patients carry tags of a second code. The local monitoring unit includes a receiving unit tuned to the frequency of the signals transmitted by the transmitting tags. Typically the local monitoring unit further includes a microprocessor to allow local processing of the data before sending it to the central monitoring station. The communication between local monitoring units and a central monitoring unit may be either wireless communication, e.g. RF, or by conventional communication lines such as telephone lines, cable TV, WAN, LAN, etc.
When used for monitoring persons, the portable tag is usually strapped around a limb of the person being monitored and typically includes various sensors for sensing tampering with the tag and other activities of the monitored person. The sensors are tested periodically and corresponding signals, including the tag identification code and the sensors data, are broadcast periodically to be received by one or more local monitoring units, whereby they are processed and optionally reported to the central monitoring station. Current tags typically include microprocessors which enable programming the operation of the tag with regard to various parameters in order to meet the requirements specific to the subject to whom the tag is attached. Thus, parameters such as sampling intervals, data transmission intervals, monitored time periods, permitted and barred locations, etc., can be selected according to specific the needs.
U.S. Pat. Nos. 5,504,474, 5,831,535 and 5,936,529, all assigned to the present assignee and incorporated herein by reference, including drawings and references cited therein, disclose a tamper-resistant tag of the type described above, for use with monitoring systems. U.S. Pat. No. 5,936,529 further teaches a manual resetting device which, when connected to the tag, enables external reprogramming of the tag by authorized parties. Thus, program parameters can be easily reset for reuse with another subject.
Generally, monitoring systems are operated under two basic configurations. One configuration, consists of separate independent local monitoring systems, each comprising a local monitoring unit dedicated to one or more tag carriers which are confined to a pre-determined location. The confined area can vary in size and accordingly the strength of the signal emitted from the tag and/or the reception level of the local receiver are chosen to fit the specific area. The local monitoring units may report to a central monitoring station where information from separate stations is collected and compared to the specific program requirements put on the specific monitored person. Alternatively, a local monitoring unit can be an independent station where data is processed for further action. Monitoring systems of this type are used for example for criminal offenders under house arrest, where the offender is required to stay in a pre-designated location or for Alzheimer patients where there is a danger of the patient getting lost, etc. Typically the pre-designated location is the monitored person residence.
Another configuration is an area monitoring system (AMS) where a network of receivers “covers” a restricted area in which a plurality of tag carriers are moving. Such systems are employed in building facilities and surrounding, for example hospitals, rehabilitation centers etc., where a large number of persons are monitored within the same area. The local receivers in an area monitoring system are arranged such that the receiving range of each receiver covers a certain part of the whole area. Preferably the zones covered by adjacent receivers overlap such that the signals transmitted by tags are received by more than one receiver. The data collected from all receivers is reported to a central monitoring station where, by applying various methods, the location of each of the tag carriers is determined to more or less degree of accuracy. Such methods may employ triangulation calculations based on signal strength analysis, time-of-arrival analysis, angle-of-arrival analysis or combinations thereof. Simpler “cell based” methods may use a set of rules based on knowledge of the coverage area of each of the receivers and of overlapping regions. However, known methods suffer from a number of drawbacks. Triangulation methods may involve special relatively expensive technology such as direction-finding receivers and may also suffer from inaccuracy due to screening and reflecting effects, especially when used indoors. The simpler “cell based” methods are inherently limited by the number of the local units distributed within the monitored area and their coverage area. The tracking and locating ability of monitoring system, i.e., the ability to continuously locate the position of individuals as they move throughout a restricted zone, depends on the space and time resolution of the information received. Obviously, the higher the number of receivers distributed within a confined area and the shorter the time intervals between successive signals, the better is the tracking resolution. However, expense consideration put constraints on the number of receivers and power consumption consideration limit the signal transmission repetition rate. There is therefore still a need for improving tracking capability of monitoring systems.
The present invention, by adding a novel feature within the existing basic structure of a transmitting tag, provides enhancement of tracking resolution of monitoring system in both time and space, without increasing significantly power consumption. Furthermore, the novel feature of the present invention provides other benefits such as, for example, control over accessibility to particular zones and/or equipment within a restricted area. Thus, the transmitting tag of the present invention not only offers the advantage of enhanced tracking but can also be used for enhancing control over the movements and actions of the monitored subject.